171 Y^7 



R 









/ 



Tfi 407 
.T58 
Copy 1 



AMERICAN SOCIETY OF CIVIL ENGINEEES. 

INCORPORATED 1852. 



Note. — This Society is not responsible, as a body, for the facts and opinions advanced in any 
of its pubhcations. 

NOTE OX 

THE RESISTANCE OF MATERIALS, 

AS AFFECTED BY FLOW AND BY RAPIDITY OF DISTORTION. 

A Paper by Prof. PvObeet H. Thukston, Member of the Society. 

Pbesented Maech 1st, 1876. 



The effect of the "Flow of Metals" and of the force of polarity de- 
scribed by Prof. Henry, in modifying their resistance to external stress 
and their strain, was alluded to by the writer in preceding Transactions, 
as follows :* 

" The same molecular movement, or flow, which rearranges the inter- 
nal force and relieves internal strain, may be a phase of that viscosity 
which Yicat sui^posed might in time permit rupture of metal subjected 
to stress nearly approaching its original ultimate resistance, the one 
action being a more immediate result than the other, and the latter ]pro- 
ducing its effect, even when cohesive force may have been actually inten- 
sified." 

It was noted, however, that, in all cases in which wrought iron and 
steel had been subjected to stress exceeding the elastic limit, the metal 
had exhibited no tendency to flow, and that, in nearly every case ob- 
served, an actual "elevation of the elastic limit by strain" had taken 
place. No experiment had then been made by the writer in which the 
same sample had exhibited both the elevation of the elastic limit by 
strain and the phenomenon of flow. 

Since that time, when experimenting upon copper, strain- diagTams 
produced automatically have been observed to exhibit this double effect. 
The elevation of the elastic limit has occurred in the earlier part of the 
test, and, at a later period, the strain- diagram exhibits flow, the metal 
yielding under a gi'adually decreasing stress. The progressive distortion 
which had never been observed by the writer in iron or steel, has, since 
the date of the paj)er, been frequently noted in other materials. For 
example, the following are a few illustrati6ns f : 

* LXXXII. On the meclianical Properties of Materials of Construction. Vol. Ill, page 13. 
t Selected from the record books of the Mechanical Laboratory of the Stevens Institute of 
Technology. 



'KjUaT 



y^.'.'^i 



\ 



Tests by Toesiox. 



•A'^ 
A^ 



•y»^^ 



NUM- 



OF 

Test. 



Material. 
Parts 



Tin. ^Copper. 



Time 


Angle 


UNDER 


OF 


; Stress. 


Torsion. 



Fall 

OF 

pencil. 



11 


o 










21- 


Ph 


3 

4 




5 




6 





100 



... 40 hours. 65° 0.06 inches. Recov'd after further distortion of 1= 

; 1 hour. 180= 0.1 " " in 8=. 

2 hours. 280= 0.1 " " in 80°. 

44 I 0.56 12min's. * 380= 50 per cent. Did not recover, 

89' 1.11 Behaved like No. 4. 

Alloy. 58= 0.2 inches. Did not recover. 

Tests by Teaxsyeese Steess, — t\t:th Dead Loads. 

Samples 1 X 1 X 22 inches. 



Number 

OP 

Test. 



Material. 
Parts 



Load. Deflection. 
Pounds. Inches. 



Time 



Tin. Copper. 



Increased 

Deflection. 

Inches. 



Breaking 
Weight. 
Pounds. 



7 




100 
98.1 


600 
475 


0.534 
1.762 


5 minutes. 
3 


0.009 
0.291 


650 


8 


1.9 










500 


2.108 


3 " 


0.488 


500 


9 


7.2 


92.8 


950 


0.348 


5 


0.081 


135a 


10 


10. 


90. 


950 


0.395 


5 '« 


0.021 










■ 1485 


3.447 


13 


4.087 


148^ 


11 


90.3 


9.7 


100 


0.085 


10 .«« 


0.021 


1 








120 


0.14 


10 


0.055 










140^ 


0.221 


10 


0.098 










« 


0.319 


10 


0.038 










" 


0.357 


40 hours. 


0.92 




/ 






160 


1.294 

1.32 

2.32 


10 minutes. 
Iday. 
1 " 


0.025 

1. 

1. 




/ 






" 


2.32 


1 " 


1. 


160 


12 


98.89 


1.11 


90 


' 0.243 


5 minutes. 


0.063 










120 


0.736 
1.791 
2.539 


30 
45 


1.055 
0.748 
0.595 












3.134 


12 hours. 


8. 


120 


13 


100 




80 


0.218 


5 minutes. 


0.064 


110 



* Taking elasticity line. 



3 

Metals having a composition intermediate between these extremes 
have not been observed to exhibit flow or to increase deflection under a 
constant load. 

Tests by tension with similar materials exhibit similar results, and 
these observations and experiments thus seem to confirm the remarks of 
the writer as above quoted, and to indicate that, under some conditions, 
the phenomena of flow and of elevation of the elastic limit by strain may 
be co-existent and that progressive distortion may occur with "viscous " 
metals. 

The paper referred to, enunciated a principle which had been deduced 
,from experiments on wrought iron which is, if possible, of more vital im- 
portance to the engineer than the facts just given, viz. : " That the time 
during which api^lied stress acts, is an important element in determining 
its effect, not only as an element which modifies the effect of the vis viva 
of the attacking mass and the action of the inertia of the i^iece attacked, 
but, also, as modifying seriously the conditions of production and relief 
of internal strain by even simple stresses."* 

It was then shown, by autographic strain-diagrams, that some mate- 
rials yield the more readily the more rapidly the distortion and rupture 
are produced, their resistance varying in some inverse ratio with the 
rapidity of change of form. It was further suggested that this action 
might be closely related to the opx^osite phenomenon of the elevation of 
the elastic limit by strain. An explanation was offered in the theory that, 
mth rapid distortion, insufficient time is allowed for the relief of internal 
strain in materials capable of exhibiting that condition. It was further 
remarked that "the most ductile substances may exhibit similar behavior, 
when fractured by shock or by any suddenly applied force, to substances 
which are comparatively brittle," and illustrations were given of such 
behavior, and the precautions to be taken by the engineer, in view of this 
important modification of the resistance of materials by velocity of rup- 
ture, were stated. 

The writer has continued his experimental researches, with occasional 
inteiTuption, since that time, and has found the above given statements 
confirmed, and that relations exist between these phenomena of strain 
and the time under stress, which may properly be stated here as comple- 
mentaiy of the principles already published in the two xoreceding notes 
which have appeared in Transactions.! 

* Vol. Ill, page 30. t LXI. Vol. II, page 239. CXV. Vol, IV, page 334. 



Should it be true, as suggested by the writer, that the cause of the 
decreased resistance, sometimes observed with increased velocity of dis- 
tortion, is closely related to the cause of the elevation of the elastic limit 
by strain,-^ it would seem a simple corollary, that materials so inelastic 
and so viscous as to he incapable of becoming internally strained during dis- 
tortion should offer greater resistance to rapid than to slowly produced dis- 
tortion, in consequence of their inability to " flow " so rapidly as to reduce 
resistance by such fluxion at the higher speed, or by correspondingly 
reducing the fractured section. This principle has been shown, by a 
large number of experiments, to be frequently, if not invariably, the fact. 
Copper, tin and other inelastic and ductile metals and alloys are found to 
exhibit this behavior, and are, therefore, quite opposite in this respect to 
ordinary wrought iron and worked steel. 

The ^vriter has noted the fact that very soft wrought iron does not 
always exhibit an observable elevation of the elastic limit by strain, and 
Com. L. A. Beardslee, U. S. N.,f has recently observed that the softest 
and most ductile specimen of iron yet tested by him at the Washington 
Navy Yard exhibited a perceptible increase of resistance with a consider- 
able increase of rapidity of extension. This metal was peculiar in its 
softness and extreme extensibility. All the irons of commerce appear to 
loelong to the other class. 

The records of the Mechanical Laboratory of the Stevens Institute of 
Technology frequently illustrate the proposition that, metals which gradu- 
ally yield under a constant load offer increased resistance with increased 
rapidity of rux^ture. 

The curves of deflections of a considerable number of ductile metals 
and alloys are very smooth when the time during which each load has 
been [left upon them is the same ; but, whenever that time has been 
variable, the curve has been irregular. Bars of such metals broken by 
transverse stress give a greater resistance to rapidly increasing stress 
than to stress slowly intensified. Tavo pieces of tin from the same bar 
were broken by tension, the one rapidly and the other slowly. The first 
broke under a load of 2 100 and the latter of 1 400 pounds. The example 
illustrates well the very great difference which is possible in such cases, 
and seems, to the writer, to indicate the possibility in extreme cases of 
obtaining results which may be fatally deceptive when the time of rup- 
ture is not noted. 

♦Transactions, Vol. III,. page 363.. t Whose work has been referred to, in earlier papeiHS. 



Antograpliic strain-diagrams, given by this class of metals, exhibit 
smooth, straight and horizontal lines for long distances on the paper 
where the distortion is produced by a uniform motion. Increasing the 
rax^idity of distortion causes an immediate and sustained elevation of the 
pencil, and'a decrease of velocity causes the line to droop to a lower level, 
In some experiments "^ a torsion of one revolution in a half hour, the 
test jDiece being f inch diameter and one inch long, just kept the pencil 
on a horizontal line. 

Two test pieces from the same bar were broken, the one rapidly, 
the other slowly. The former gave a strain-diagram of which the 
maximum ordinate was about 50 foot pounds higher than the maxi- 
mum of the latter, the difference being nearly 50 per cent, of the 
higher, f 

It is evident that, whatever the character of the material and what- 
ever the velocity of rupture, the effect of the inertia of the mass, and of 
particles not immediately affected by a shock, remains, and that its effect 
is always to reduce the resilience of the metal and its resistance to shock ; 
and this reduction may, in many cases, more than compensate the 
increase of resistance here noted. Its tendency is always to produce a 
sharp fracture which, with such sudden blows as are given by cannon 
shot, for example, may resemble the break characteristic of brittle and 
non-ductile substances. 

The wi'iter would, therefore, divide the metals used in construction 
into two classes : 

1st. Metals subject to internal strain by artificial manipulation 
and which may exhibit an elevation of the elastic limit by strain 
and decreased power of resisting stress under increasing rajDidity of 
distortion. The ordinary irons of commerce are typical of this 
class. 

2d. Metals of an inelastic viscous character, not subject to internal 
strain and not usually exhibiting an elevation of the elastic limit by strain 
and which offer increased resistance when the rapidity of distortion is 
increased. Tin is a typical examjjle of this class. 

It is ob"\T.ous that the value of the former class for the construction of 
the engineer is vastly greater than the latter, and especially for permanent 
loads and low factors of safety. 

* Made for the wi-iter with great care and skill by his assistant, Mr. Wm. Keut. 

t The inertia of the weight in these examples, has no measurable effect in modifying those 

results. 



1 



The depression of the elastic Hmit has been observed previously in ma- 
terials, but less attention has been paid to it than the importance of the 
phenomenon would seem to demand. The accompanying plate exhibits 
the strain diagrams produced by plotting the results of experiments.* 
They are selected as typical examples, and as representing the two classes 
of materials described. 

In making the experiments the bar was mounted on cylindrical steel 
bearings, which were themselves supported on accurately planed level 
surfaces, and the deflection was produced by means of a powerful screw 
and a large hand-wheel. The weight was measured by a Fairbanks 
scale combination, and the deflections and sets by a special measuring- 
apparatus f which reads to 0.0001 inch, with an error of 0.000741. 
Touch is indicated by a delicate Stackpole level. The measuring instru- 
ment was unaffected by the forces tending to distort the straining appa- 
ratus. The deflecting force was adjusted by the scale-beam. The bar 
being in place, the weight to be put on it was set off on the scale-beam, 
and the screw was carefully turned until, by its pressure on the middle 
of the bar, the scale-beam slowly rose and vibrated about the middle of 
its range, which point was indicated by a pointer at the end of the beam, 
traversing a fine lined scale on the frame. When the adjustment had 
become satisfactory, the deflection was read off and the beam usually 
released, in order that the set might be observed. It was then again 
deflected by a heavier weight. Occasionally the bar was left thus strained, 
and with a constant deflection, for a considerable ]3eriod of time, and 
the change of effort exerted by it noted at frequent intervals. In all such 
eases the scale-beam gradually drooped, and a decreased efibrt to effect 
restoration of form was indicated. When the beam had fallen, the 
weight was pushed back until the beam arose and vibrated about the 
centre line again, and the weight and time were recorded. This was 
repeated as the beam exhibited less and less loss of power of restoration, 
and when this decrease of effort no longer exhibited itself, a new 
series of deflections was produced. 

The bar No. 599, which was quite ductile, exhibited an unchanged 
law of relation of amount of deflection to intensity of deflecting 
force, and, as shown by the diagram, the curve representing its test 
pursued the same general direction after one of these "time-tests" as 
before. 



* Made and recorded in the Mechanical Laboratory of the Stevens Institute of Technology, 
t Made to the order of the writer, by Mess. Brown & Sharpe. 



8 

The loss of effort at 163 pounds is seen to have been about 20 pounds, 
the deflection amounting to 0.0347 inches, and the effort falling from 165 
to 143 pounds. At 403 pounds the loss of restorative force is about the 
same ; the figures fall from 403 to 333 pounds, the deflection being held 
constant at 0.0886 inches, again from 333 to 302 pounds at a deflection of 
0.0896, and still again from 1233 to 1137 pounds at a deflection of 0.5209 
inches. 

Before the bar, under further deflection, had quite regained its original 
resisting power, the "time-test" was repeated, the deflection amounting 
to 0,5456 inch, and the weight api^lied being 1233 pounds. The result 
noted was quite unanticipated. The effort steadily decreased at a vary- 
ing rate, which is indicated by the diagram of time and loads, and the 
bar finally snapi)ed shai^^ly, and the two halves fell uj^on the floor. The 
effort had decreased to 911 pounds. The deflection was precisely -what 
it had been under the load of 1233 jDounds. The beam had balanced at 
911 pounds for about three minutes when the fracture took place. An 
assistant w^as sitting fifteen or twenty feet from the machine at the in- 
stant, but no one had approached the machine after the last adjustment- 
of the weight. 

This is a case without parallel in the experience of the writer, and its 
conclusion indicates a possibility of depreciation in resisting power of the 
class of metals of which tin has been taken as the type, which deprecia- 
tion, in the present state of our knowledge of the properties of such 
metals in this regard, it may be safest to assume to be a source of danger 
in some cases in which the load approaches the maximum resisting x^ower 
of the piece. This illustrates the case of progTession of flow until the 
section most strained has been weakened to the point of actual molecular 
disruption, which disruption would seem to have been here produced by 
the effort of other and less injured portions, to resume their original 
positions, and to straighten the two halves of the bar. It would seem 
that such action should be determined by flow occurring in a somewhat 
ductile but still somewhat elastic metal. 

The strain diagxam of this bar is seen to be nearly hyperbolic ; but 
the law of Hooke, nt tensio sic vis, holds good, as usual, up to a point at 
which the load is about one-half the maximum. The curve of times and 
loads, exhibits the rate of loss of effort while the bar was finally held 
at a deflection of 0.5456 inch, the load being carefuUy and regiilarly re- 
duced, as the effort diminished, from 1233 to 911 pounds, at which. 



latter figure the bar broke. The curve is a very smooth one. The fol- 
lomng is the record of the test : 

Bae No. 599. 

90 parts zinc, 10 parts copper : 1 X 0. 992 X 22 inches. 



Load; 



Inches. 



23 
43 

63 
103 
143 

163 ! 
Kesistance 
to U3 



163 

203 I 

243 j 

283 I 



0.0033 

0.0078 

0.0127 

0.0225 

0.031 

0.0347 

fell in 15 h. 25 m. 

0.0347 ' 

0.0039 

0.0391 

0.0471 

0.0544 I 

0.0611 

0.0692 



Load. 
Pounds. 



363 I 0.0781 

403 I 0.0881 
i 
3 I 0.0079 

403 I 0.0886 
Eesistance fell in 8 li. 30 m. 

to 333 0.0886 ] 

3 0.0246 

333 0.0896 

Besistance fell in 15 li. 



to 302 
303 
403 
503 
603 



0.0896 
0.0876 
0.1072 
0.1282 
0.1521 



3 
643 
803 
1003 
1103 
1203 
1233 



0.1641 

0.2149 

0.3178 

0.3921 

0.481 

0.5209 



0.033& 



Kesistance fell in 15 m. 



to 1 137 

3 

1137 

1233 



0.5209 



0.5131 
0.5456 



0.2736 



The bar was left under strain at 11 h. 22 m. a. m. , and the eftort to 
restore itself measured, at intervals, as follows : 

Hour.— 11 h. 37 m.; 11 h. 50 m. a. m. 121i. 2 m.; 12h. 8 m.; 12 h. 25 m.; 12 1i. 39|m.; 
12 h. 53>^ m.; 12 h. 58^ m.; 1 h- 20 m. p. ii. 

Effort.— 1 133; 1 093; 1 070; 1 063; 1 043; 1 023; 1 003; 993; 911 pounds. 

At 1 h. 23 m. p. M. the bar broke. 

An examj)le of somewhat similar behavior, but exhibited by a metal 
of very different quality, is shown on the next page. 

This bar was hard, brittle and elastic, but must apparently be classed 
with tin in its behavior under either continued or intermitted stress. 

There seems to the writer to exist a distinction, illustrated in these 
cases, between that "flow" which is seen in these metals, and that, to 
which has been attributed the relief of internal stress and the elevation of 
the elastic limit by strain and T\'ith time. 

This last phenomenon — the exaltation of the elastic limit by strain — 
has been obseiwed very strikingly, by the T^Titer, in the deflection of 
ii-on bars, by transverse stress. The plate exhibits the strain -diagrams 



10 



Bar 596. 

75 parts zinc, 25 parts copper; Second casting : 0.985 X 0.985 X 22 inches. 



Load; 


Inches. 


Load; 
Pounds. 


Inches. 


Load; 
Pounds. 


Inches. 


Tounds. 


Deflection. 


Set. 


Deflection. 


Set. 


Deflection. 


Set. 


23 


0.0057 

0.0142 

0.0207 

0.0275 

0.0346 

0.0414 

0.0485 

0.0549 

0.061 

0.G669 





1 

423 

463 

503 

3 

503 


0.073 

0.0799 

0.0866 


0.0014 


i to 473 

3 

503 

543 

583 

603 

623 

643 

663 

Broke 5 
sounc 


0.0866 




63 


0.0092 


103 


0.0894 
0.0952 
0.1012 
0.1042 
0.1075 
0.1102 
0.1136 




143 




183 


n nsfifi 




223 


Eesistannft fell in 5 h. 




263 


to 489 
3 
489 
Besistai 


0.0866 




0.0074 
h. 30 m. 




303 




343 


0.0866 
ice fell in 13 




383 


sec. after with ringing 



obtained by transverse deflection of 4 bars of ordinary merchant wrought 
iron which were all cut from the same rod. Of these, two were tested in 
ihe machine above described, in which the deflection remains constant 
when the machine is untouched while the load gradually decreased — or, 
more properly, while the effort of the bar to regain its original form, 
decreases. The other two were tested by dead loads — the load remaining 
constant while the deflection may vary when the apparatus is left to 
itself. (The record is given on pages 209-212. ) . 

These two pairs of specimens were broken ; one in each set by adding 
weight steadily until the end of the test, so as to give as little time for 
elevation of elastic limits as was possible, and one in each set by inter- 
mittent stress, observing sets, and the elevation of the elastic limit. 

If the long-known effects of cold-hammering, cold-rolling and wire- 
drawing, in stiffening, strengthening and hardening some metals can be, 
as the writer is inclined to believe, attributed in part to this molecular 
-change, as well as to simple condensation and closing up of cavities and 
pores, this exaltation of the elastic limit by distortion under externally 
applied force, has now been shown to occur in iron and in metals of that 
class in tension, torsion, compression and under transverse strain. 

Eeferriug to the plate, it wiU be seen that there is exhibited the 
action in the latter case even more fuUy and strikingly than in the 
record above given, and a study of these typical examples cannot fail to 
l^rove both interesting and instructive. 



11 

Tests of wrought Irox Bars by Transverse Strain. 

Samples 1 inch square, 28 inches long : 22 inches between supports. 

No. 648. Tested in Fairbanks' Machine. 



Load; 
pounds, 



Inches. 



Deflec- 
tion. 



Set. 



103 0.0132 j 

203 I 0.0244 1 

Resistance fell in 13 h. 35 m. 
to 199 0.0244 

303 0.0342 

403 j 0.0428 
Kesistance fell in 1 h. 



m. 



to 399 



503 



0.0428 

0.0042 

0.0528 

0.0619 

Resistance fell in 4 h. 
to598 i 0.0619 

803 I 0.0806 ! 

I i 

Resistance fell in 15 h. 15 m. 



to 789 



903 I 0.0907 

' 1 
1003 0.0995 ' 

I 

Resistance fell in 5 h. 20 m. 

to987 i 0.0995 

3 I : 0.0049 

1203 I 0.1197 

3 0.0071 

1203 0.121 

Resistance fell in 2 h. 
to 1187 0.121 



1203 
1243 
1283 
1323 



0.1226 
0.1266 
0.1301 
0.1354 



0.0096 



Load: 



Inches. 



pounds. Deflec- 

i TION. 



1 363 : 0.1421 
1403 I 0.1504 



1 403 j 0.1522 
Resistance fell in 3 m. 



Set. 



0.0196 



Resistance fell in 6 h. 

I 
to 1457 1 0.287 



1457 
1603 
1 703 



0.2863 
0.3016 
0.3921 



0.2431 



1703 0.4301 

Resistance fell in 20 h. 50 m. 

tol541 0.4301 

3 j 0.2846 

1541 ' 0.4296 



Load; 
pounds. 



to 1 387 


0.1522 
:e fell in 2 

0.1522 
36 fell in 3( 

0.1522 




Resistan 
to 1 361 


1. 25 m. 


Resistan 
to 1 329 


) h. 5 m. 


3 


0.0246 


1329 


0.1451 

0.1522 

0.16 

0.1647 

0.1761 

0.2548 




1403 




1483 




1 523 




1 563 




1 603 





3 


0.1091 


1 603 


0.287 










Inches 



Deflec- i 

TION. I 



Set. 



1 603 0.4346 
1 711 0.4456 
1 753 0.4513 
1 781 0.4651 
Resistance fell in 6 h. 3 m. 
to 1 661 0.4651 

3 0.3106 

1 675 0.4676 
1 787 0.4808 
1 811 0.5446 

3 

1811 0,5661 

Resistance fell in 46 m. 

to 1675 0.5661 

Resistance fell in 17 h. 
to 1661 I 0.5661 



0.3771 



1661 
1801 
1861 
1877 
1891 



0.5645 

0.578 

0.5886 

0.6034 

0.6626 



0.4081 



1891 I 0.7001 
Resistance fell in 10 s. 

tol80lj 0.7001 

Resistance fell in 6 m. 

tol737| 0.7001 

Resistance fell in 5 h, 23 m. 

tol721j 0.7001 i 

3 1 0.5406 



12 



No. 6i8.— (Continued.) 



Load; 
pounds. 



1741 
1911 
1921 
3 
1921 



Indies. 



Deflec- 
tion. 



0.7031 
0.7246 
0.7566 



0.7746 



Set. 



0.5746 



Besistance fell in 21 h. 48 m. 



1767 


0.7746 


3 




1767 


0.7726 


1931 


0.7876 


1995 


0.8036 


2 001 


0.8266 


3 




2 001 


0.8498 



0.6028 



0.6451 



Besistance fell in 21 h. 30 m. 



to 1 831 


0.8498 


3 




1831 


0.8471 


2 003 


0.8641 


2 071 


0.8819 


2 081 


0.9396 


3 




2 081 


0.9886 



0.6780 



0.7576 



Besistance fell in 21 li. 39 m. 



to 1 871 


3 


1911 


2 083 


2 121 


2 131 


3 


2 131 



0.9904 
1.0106 
1.0496 
1.0911 



1.1316 



0.8148 



0.9021 



Load; 
pounds. 



Inches. 



Deflec- 
tion. 



Set. 



Resistance fell in 47 h. 37 m. 



to 1 869 
3 
1941 
2 131 
2 181 
2 201 
2 211 
3 



1.1316 



0.958 



1.1358 
1.1551 
1.1686 
1.1981 
1.2356 



1.0361 



Besistance fell in 9 h. 



to 1 997 



1.2356 



2 001 


1.3016 


2 211 


1.3326 


2 231 


1.3656 


2 237 


1.3936 


3 




2 241 


1.4441 



1.1946 



Resistance fell in 13 h. 50 m. 



to 2 041 
3 
2 041 
2 241 
2 281 
2 301 
2 311 
3 
2 311 



1.4441 



1.4421 
1.4631 
1.4821 
1.5216 
1.5531 



1.6166 



1.2538 



Resistance fell in 8 h. 8 m. 



to 2 091 



2 091 



1.6166 



1.6166 



1.4181 



Load; 
pounds. 



Inches. 



2 311 
2 341 
2 351 
3 
2 351 



Deflec- 
tion. 



1.6466 
1.6996 
1.7321 



2.0446 



Resistance fell in 16 h. 



to 2 135 


2.0446 


3 




2 135 


2.0431 


2 355 


2.0646 


2 391 


2.0736 


2 411 


2.1136 


3 




2 411 


2.1451 



1.8441 



1.8964 



Resistance fell in 8 h. 35 m. 

to 2 238 2.1451 

Gradually reduced strain. 

to 3* . 1.9266 

Gradually increased strain. 



to 2 238* 


2 411 


2 491 


2 501 


3 


2 501 



2.1336 
2.1516 
2.1811 
2.2121 



2.2471 
Resistance fell in 14 h, 10 m. 
to 2 295 2.2471 



3 
2 295 
2 541 
2 561 



2.2456 
2.2762 
2.3102 



2.0331 



2.0763 



* Gradually reduced strain to 3 pounds, taking a number of readings ; then gradually 
increased it to 2 238 pounds, taking readings corresponding to former ones; fouud that in> 
crease of deflection was proportional to increase of load. 



13 



No. CAS.— [Concluded.) 



Load. 
Pounds. 



Deflec- 
tion. 



2 561 j 2.35 
Resistance fell in 6 h. 18 m. 



Set. 



to 2 369 


2.35 


3 




2 369 


2.3587 


2 551 


2.3782 


2 571 


2.385i 


2 591 


2.4287 


3 




2 591 


2.5044 



2.1952 



Eesistance fell in 15 li. 4 m. 

I 
to 2 371 2.5044 1 

3 1 2.2842 

I 1 
2371 t 2.5022 



Load. 
Pounds. 



2 591 
2 611 
2 631 
3 
2 631 



Deflec- 
tion. 



2.5247 
2.5334 

2.5927 



2.653 



Set. 



Eesistance fell in 8 h. 2 m. 



to 2 371 

3 

j 2 371 

2 631 

2 651 

2 661 

I 3 

2 661 



2.653 


2.6532 


2.6833 


2.6992 


2.7307 


2.8324 



2.4227 



2.4987 



Load. 
Pounds. 



Inches. 



Deflec- 
tion. 



Set. 



Resistance fell in 61 h. 32 m. 



to 2 363 


3 


2 363 


2 685 


2 701 


2 710 


2 720 


3 


2 720 



2.8286 

2.8627 

2.871 

2.8917 

2.9297 



2.5924 



2.647 



2.9692 
Eesistance fell in 5 h. 48 m. 

to2483 2.9692 

3 2.7357 

Bar removed : test ended. 



No. 649. Tested ix Fairbanks' Machine. 



Load. 


Deflection. 


Load. 


Deflection . 


Load. 


Deflection. 


Load. 


Deflection 


Pounds. 


Inclies. 


Pounds. 


Inclies. 


Pounds. 


Inches. 


Pounds. 


Inches. 


103 


0.0139 


900 


0.0889 


1462 


0.1505 


In2f m 


. was . 3629 


200 


0.0238 


; 1000 


0.0982 


1480 


0.1569 


1620 


0.3704 


300 


0.0328 


1100 


0.1081 


' 1500 


0.1619 


1640 


0.3831 


405 


0.0425 


1200 


0.1171 


1520 


0.1709 


In 6 m 


, was 0.4404 


500 


0.0519 


1300 


0.1279 


1540 


0.1804 


1660 


0.4479 


600 


0.0602 


1 400 


0.1398 


1560 


0.2078 


1 680 (b) 


0.4599 


700 


0.0689 


1420 


0.1435 


1580 


0.2429 






800 


0.0787 


1442 


0.1472 


1 600(a) 


0.2854 


2 350 


5.577 



(a) At 1 600 pounds the beam sank instantly; ran the pressure screw down so as to keep the 
beam balanced for 2| m., with increase of deflection as noted, (b) At 1 680, ran pressure screw 
rapidly but steadily down, moving the poise along the beam to keep it balanced. The beam 
vibrated up and down, falling or rising instantly as the wheel was turned slower or faster. 
The resistance reached a maximum of 2 350 pounds, when the deflection was 5 577 inches. 



^ \^ 



No. 650. Tested by Dead Loads. 



Load; 

Pounds, 


Deflection; 
Inches. 


Load; 
Pounds. 


Deflection; 
Inches. ' 


Load; 
Pounds. 


Deflection; 
Inches. | 


Load; 
Pounds. 


Deflection 
Inches. 


100 
200 


0.015 
0.0229 


400 
600 


1 
0.0425 

0.0638 1 


800 
1200 


0.0858 

0.1456 i 

1 


1400 
1 500 (c) 


0.1749 
0.2143 



(c) At 1 626, the reading was not taken. Weights as follows were rapidly added, 4 or 5 pieces 
each minute, as follows:— 82, 25, 42, 15, 16, 10, 15.5, 16, 25, 25, 25, 13, 11.5, 16, 27, 62, 40.5, 61, 
45, 62 = 2 260.5 pounds. The bar sank rapidly, its side pressure splitting the wood which 
confined the mandrels. The set, measured after the bar was removed, was 2.5 inches. The 
total deflection is calculated as follows: — the elasticity of the bar remaining the same the in- 
crease of deflection over set is directly proportional to the load. (This is shown by the paral- 
lelism of the elasticity lines with the original liue within the elastic limit.) Thus at 800 
pounds, the set was inappreciable, deflection 0.0858; whence 800: 0.0858:: 2 260: 0.242 differ- 
ence of deflection and set: set was 2.5, hence calculated deflection 2.742 inches. 



No. 651. Tested by Dead Loads. 



—* 

Load: 


Deflection; 


Load; 


Deflection; 


Load; 


Deflection; 


Load; 


Deflection 


Pounds. 


Inches. 


Pounds. 


Inches. 


Pounds. 


Inches. 


Pounds. 


Inches. 


100 


0.0158 


In 5 h. 46 m. In 0.6598 


In48h.C 


Om.was 1.9245. 


2 452 


3.0732 


200 


0.0275 


1700 0.67 


2 222 


1.9379 


2 484 


3.0812 


400 


0.0489 


In 3 m. was 0.6716 


2 288 


2.1386 


In 39h. 40 m. 4.2591 


600 


0.0709 


" 16 h. " 0.7615 


In 12 n 


I. was 2.9535 


In 43h. 20 m. 4.2591 


803 


0.0913 


1800 


0.771 


2 266 


2. 9928 1 


2 513 


4.2623 


1000 


0.1141 


1900 


1.0904 


In 17 VL 


I. was 3.0157 


2 556 


4.267 


1 200 


0.1394 


In 3 h. 15 m. was 1.8567 


" 3h. 37 m. '« 3.0236; 


In 4 h. 20 m. 4.2749 


1400 


0.1701 


i "45h. 45 m. " 1.8709 


2 288 


3.029 


2 589 4.2749 


1500 


0.2465 


2 005 1.8787 


2 350 


3.0426 


In48h. was 4.6591 


In 8 m. 


was 0.4307 


In 3 h. was 1.8819 


2 370 


3.0433 


In61h.30m«' 4.6701 


1600 
In 6 m 


0.489 
was 0.6504 


1 2 052 
1 2 115 


1.8886 
1.8921 


In25h.l 
2 422 


5 m. was 3.0677 
3.0701 


Weights reached 
support. Test 
was ended. 



The strain-diagrams exhibited in the plate do not present to the 
eye one of the most important distinctions between the two classes 
of metals. As seen by study of these diagrams, both classes, when 
strained by flexure, gradually exhibit less and less effort to restore them- 
selves to their original form. 

In the case of the tin-class, this loss of straightening power seems 
often to continue indefinitely, and, as in one example here illustrated, 
even until fracture occurs. 



15 



With iron and the class of which that metal is typical, this reduction 
of effort becomes gTadually less and less rapid, and finally reaches a limit 
after attaining Avhicli, the bar is found to have become strengthened, and' 
the elastic limit to have become elevated. In this respect, the two classea 
are affected by time of strain, in precisely opposite ways. 

The plate exhibits, even better than the record, the superior ultimate 
resistance of the bars which have been intermittently strained, as well as 
the elevation of the elastic limit. This parallelism of the "elasticity 
lines " obtained in taking sets, shows that the modulus of elasticity is 
unaffected by the causes of elevation of the elastic limit. 

Evidence appealing directly to the senses has been presented in the 
course of experiment on the second class of metals, of the intra-molecular 
flow. When a bar of tin is bent, it emits while bending the peculiar 
crackling sound, familiarly known as the "cry of tin. " This sound has 
not been observed hitherto, so far as the ^vriter is aware, when a bar has 
been held flexed and perfectly still. In several cases recently, in exper- 
iments on flexure* of metals of the second class, bars held at a constant 
deflection have emitted such sounds hour after hour, while taking set 
and losing their power of restoration of shape. 

During some of the exi3eriments made, a very marked illustration of 
the decrease of set with time, which has been observed and described by 
Prof. W. A. Norton, has been noted, and the recovery of straightening 
power in the deflected bar has sometimes been strikingly large, amount- 
ing to nearly 30 pounds in 15 minutes. A record of one of these bars is.— 

Bab No. 563. 

17 . 5 parts copper, 82 . 5 parts tin. . 986 X . 993 X 22 inches. 



Load; 


Inches. 


1 
t 
Load: 

pounds. 


Inches. 


Load; 
pounds 


Inches. 


pounds. 


TION. S=^- 


Deflec- 
tion. 


Set. 


Deflec- 
tion. 


Set. 


10 


0.0027 




140 


0.0804 




300 


0.4597 




20 


0.007 




180 


0.1343 




' 




0.3084 


40 


0.0153 
0.0256 





200 
5 


0.1666 


0.0821 


Set decreased in 


i 


60 


, 2 hrs, 20 min. 


0.2845 


80 


0.0365 




200 


0.1798 





to 300 


0.5332 




100 


0.0499 




240 


0.2503 




310 


Bar broke in putting 


5 




0.0092 


280 


0.3762 






on strain. 



* Made in the mechanical Laboratory of the Stevens Institute of Technology, 



0-Z^p 



LIBRARY OF CONGRESS 

028 116 607 4 



16 



After 300 pounds had been placed on the bar, and the reading taken, 
the screw was run back till the beam just balanced at 5 pounds, the 
pressure block attached to the screAv just barely touching the bar. The 
set was then read, as above, 0.3084 inches, the beam slowly rising. The 
pressure screw was then run back till beam again balanced at 5 pounds, 
and the set measured 0.3022 inches. The time was 2 minutes. The 
beam again rose, poise on beam was jDushed forward and balanced at 
10 iDOunds ; the time was 2 minutes. In 2 minutes more, beam balanced 
at 14 pounds. The pressure screw was again run back till beam balanced 
at 5 j)ounds and the set measured^^?^i8^ inches," The beam rose again ; 
at 11 hours 37 minutes, A. M, In 2 minutes it balanced at 10 pounds, in 
10 minutes at 16 pounds, and in 29 minutes at 23 pounds. The beam 
was again balanced at 5 pounds, set measured 0. 2902 inches. The beam 
rose in 4 minutes. In 29 minutes the beam balanced at 14 pounds, and 
in 65 minutes more it balanced at 20 pounds. The beam was again bal- 
anced at 5 pounds and the set measured 0. 2845 inches. The total decrease 
of set in 2 hours 20 minutes was 0. 3084 — 0. 2845 = 0. 0239 inches. Then 
rei^laced 300 pounds, and read deflection 0. 5332 inches ; increased the 
23ressure, but the bar broke before 310 iDounds was reached. 



/ 



LIBRARY OF CONGRESS 



028 116 607 






HoUinger Corp. 
pH 8.5 



1 



